Increasing demand for high speed operation of the central processing unit of an electronic computer requires high speed operation of the output device, i.e. a high speed printing device, and various types of printing systems have been developed.
In one typical printing system, there is a system is which inks are supplied to the nozzle under a slight pressure so that the ink is projected in a hemispherical shape at the tip of the nozzle and is drawn in droplet form by applying an electric field between an accelerating electrode positioned a few milimeters ahead of the nozzle and the nozzle. The droplets of the ink then move toward the surface of the recording paper by applying a high electric field between the nozzle and the platen, said droplets of the ink being electrostatically deflected in both directions (right and left) to print characters or symbols on the surface of the recording paper.
As another typical printing apparatus, there is a system in which the ions produced between the electrodes receiving a high voltage are passed through the ink mists and the particles of the ink selectively adhere to the surface of the recording paper to cause printing. The present invention relates to this latter type of system.
The printing system will be described in detail. Corona discharge is utilized for ionization of the air. Application of a few thousand volts to very thin conductors causes corona discharge, and molecules such as oxygen, nitrogen or the like in the air surrounding this conductors are ionized. The ions produced around these conductors are attracted to the platen side by an electric field existing between the platen of the back surface of the recording paper and the conductor.
The ink is agitated by supersonic waves and changed into the mists having molecules 5 to 20 .mu. diameter and being suspended in the air. The mist is fed between the platen and a source of corona discharge by pneumatic pressure in the same direction and at the same speed as that of the paper being fed. Thus, the ions project into the ink mist, adhere around the mist, move in the combined directions of the electrostatic force and the mist stream and, adhere to the recording paper positioned between the platens and are impressed thereon.
The configuration of this system is shown in the block diagram of FIG. 1 and comprises two parts: a main body 11 and a control part 12, the main body 11 having a paper feeding device 13, printing part 14, mist generating part 15, ink circulating device 16 and mist treatment device 17, and the control part 12 having control circuit 18 and driving circuit 19 for the mist generating device.
Thus, in the above-mentioned high-speed printing apparatus, the printing capacity, i.e. a number of characters which can be printed in one row, is set at approximately 136 characters, so that if the printing operation is conducted on the recording paper having a narrow printing width, there are some disadvantages in that disturbance of the air stream at both end portions of the recording paper by the paper feeding sprockets holes or the ends of the paper cause the portions adjacent to the sprocket holes of the recording paper or back bars and the aperture plate or the like to become soiled so that the characters become blurred, faded and unclear.